Bona Fide Evidence for Natural Vertical Transmission of Infectious Salmon Anemia Virus in Freshwater Brood Stocks of Farmed Atlantic Salmon (Salmo salar) in Southern Chile

Abstract

Infectious salmon anemia (ISA) is a severe disease that affects farmed Atlantic salmon (Salmo salar), causing outbreaks in seawater in most salmon-producing countries worldwide, with particular aggressiveness in southern Chile. The etiological agent of this disease is a virus belonging to the Orthomyxoviridae family, named infectious salmon anemia virus (ISAV). Although it has been suggested that this virus can be vertically transmitted, even in freshwater, there is a lack of compelling experimental evidence to confirm this. Here we demonstrate significant putative viral loads in the ovarian fluid as well as in the eggs of two brood stock female adult specimens that harbored the virus systemically but without clinical signs. The target virus corresponded to a highly polymorphic region 3 (HPR-3) variant, which is known to be virulent in seawater and responsible for recent and past outbreaks of this disease in Chile. Additionally, the virus recovered from the fluid as well as from the interior of the eggs was fully infective to a susceptible fish cell line. To our knowledge, this is the first robust evidence demonstrating mother-to-offspring vertical transmission of the infective virus on the one hand and the asymptomatic transmission of a virulent form of the virus in freshwater fish on the other hand. IMPORTANCEThe robustness of the data presented here will contribute to a better understanding of the biology of the virus but most importantly will constitute a key management tool in the control of an aggressive agent constantly threatening the sustainability of the global salmon industry.

Recent genetic changes in enhanced populations of sea trout (Salmo truttam.trutta) in the southern Baltic rivers revealed with SNP analysis

“…Accidental or deliberate introductions of exotic and invasive species to new environments, often beneficial economically, causes distortions in the functioning of local ecosystems and can threaten native populations of fish and shellfish, as in the case of brown trout in Japan (Hasegawa and Maekawa 2008), Patagonia (Vigilano et al 2007;Young et al 2010) and in North America (Turek et al 2016), mussel Mytilus in Europe and South Africa (Kijewski et al 2009;McQuaid et al 2015 and oyster Crassostrea gigas (Carlton 1979;Meehan et al 1989;Miller et al 2012;Lallias et al 2015). Stocking and introductions to marine farms can also be the means of spreading diseases, as in salmon in Chile (Murray 2013;Marshall et al 2014) and oyster Crassostrea gigas in Europe (Mineur et al 2014). The application of genetic research facilitated more effective stocking e.g.…”

Chemical Synthesis and In Vitro Evaluation of a Phage Display-Derived Peptide Active against Infectious Salmon Anemia Virus

“…On the other hand, the recent detection of infective ISAV in the ovarian fluid and unfertilized eggs of systemically infected brood stocks devoid of clinical signs suggests the worrying possibility that vertical transmission may also occur (11). All epizootic outbreaks are caused by viral strains with deletions in a specific highly polymorphic region (HPR) of segment 6 in the viral genome (12).…”

Immune-Endocrine Interactions in the Fish Gonad during Infection: An Open Door to Vertical Transmission

“…On the other hand, some fish viruses have not been detected in any reproductive organ or cell but are still thought to be transmitted vertically since they have been found in embryos or gonadal fluids. An example is the infectious salmon anemia virus (ISAV), which was not detected in Atlantic salmon (Salmo salar) gonads but was detected in ovarian fluids and eggs [124,125]. …”